Abstract:

A chip scale package (CSP) device includes a CSP having a semiconductor
die electrically coupled to a plurality of solder balls. A can having an
inside top surface and one or more side walls defines a chamber. The CSP
is housed in the chamber and is attached to the inside top surface of the
can. A printed circuit board is attached to the solder balls and to the
one or more side walls to provide support to the CSP and to the can. The
CSP may be a Wafer-Level CSP. The can may be built from a metallic
substance or from a non-metallic substance. The can provides stress
relief to the CSP during a drop test and during a thermal cycle test.

Claims:

1. A chip scale package (CSP) device, comprising:a CSP having a
semiconductor die electrically coupled to a plurality of solder balls;
anda can having an inside top surface and one or more side walls defining
a chamber, the CSP being housed in the chamber and being attached to the
inside top surface of the can.

2. The CSP device according to claim 1, further comprising a metallic
layer formed on the semiconductor die, the solder balls being attached to
the metallic layer.

3. The CSP device according to claim 1, wherein the CSP is a Wafer- Level
CSP.

4. The CSP device according to claim 1, wherein the can is made from a
metallic substance.

5. The CSP device according to claim 1, wherein the can is made from a
non-metallic substance.

6. The CSP device according to claim 1, wherein the side walls are spaced
from the CSP by a selected distance.

7. The CSP device according to claim 1, wherein the inside top surface of
the can is square.

8. The CSP device according to claim 1, wherein the inside top surface of
the can is rectangular.

9. The CSP device according to claim 1, further comprising an opening
formed on a top surface of the can.

10. A chip scale package (CSP) device, comprising:a CSP having a
semiconductor die on which a layer of metal is formed;a plurality of
solder balls attached to the layer of metal, the semiconductor die being
electrically coupled to the solder balls; anda can having an inside top
surface and one or more side walls defining a chamber, the CSP being
rigidly attached to the inside top surface and being housed in the
chamber.

11. The CSP device according to claim 10, wherein the inside top surface
of the can is attached to the semiconductor die.

12. The CSP device according to claim 10, wherein the CSP is a Wafer-
Level CSP.

13. The CSP device according to claim 10, wherein the can is made from a
metallic substance.

14. The CSP device according to claim 10, wherein the can is made from a
non-metallic substance.

15. The CSP device according to claim 10, wherein the inside top surface
of the can is square.

16. The CSP device according to claim 10, further comprising an opening
formed on a top side of the can.

17. A chip scale package (CSP) device, comprising:a plurality of CSPs each
having a semiconductor die electrically coupled to a plurality of solder
balls; anda can having an inside top surface and one or more side walls,
the can having one or more interior walls defining a plurality of
chambers, each CSP being housed in a respective chamber and being
attached to the inside top surface.

18. The CSP device according to claim 17, further comprising a layer of
metal formed on the semiconductor die, the solder balls being attached to
the layer of metal.

19. The CSP device according to claim 17, wherein the CSP is a Wafer-Level
CSP.

20. The CSP device according to claim 17, wherein the can is made from a
metallic substance.

21. The CSP device according to claim 17, wherein the can is made from a
non-metallic substance.

22. A semiconductor device, comprising:a semiconductor die electrically
coupled to a plurality of solder balls, the semiconductor die being
encapsulated in an encapsulating compound; anda can having an inside top
surface and one or more side walls defining a chamber, the encapsulated
semiconductor die being housed in the chamber and being attached to the
inside top surface of the can.

23. A method for manufacturing a chip scale package (CSP) device,
comprising:forming a frame having a plurality of spaced apart chambers
each sized to house a CSP;attaching a respective CSP to each of the
chambers; andcutting the frame containing the plurality of CSPs into a
plurality of CSP devices, each CSP device having a CSP capped with a can.

24. The method according to claim 23, wherein the frame is made from a
metallic substance.

25. The method according to claim 23, wherein each of the CSPs includes a
semiconductor die electrically coupled to a plurality of solder balls.

Description:

FIELD OF THE INVENTION

[0001]The invention relates to semiconductor packaging, and more
particularly the invention relates to a Chip Scale Package (CSP) with a
can attachment.

BACKGROUND

[0002]CSPs are used in a wide variety of consumer electronics products. In
particular, Wafer-Level CSP (WL-CSP)s are used in mobile phones, PDAs,
lap top computers, printers and other applications. The WL-CSP integrated
circuit (IC) is attached to a printed circuit board (PCB) by, for
example, a conventional surface mount technology. The pads of the IC
connect directly to the pads of the PCB through individual solder balls
and thus do not require underfill encapsulation material.

[0003]The WL-CSP offers several advantages over other types of CSPs (e.g.,
ball grid array-type, laminate-type). The WL-CSP does not require bond
wires or interposer connections between the IC and the solder balls.
Since the WL-CSP IC pads connect directly to the PCB, the inductance
between IC and the PCB is minimized thereby improving signal quality.

[0004]After a device having a WL-CSP attached to a PCB is built, the
device is subjected to a drop test to measure its durability. The drop
test is a technique for measuring the durability of a component by
subjecting it to a free fall from a predetermined height onto a surface
under prescribed conditions.

[0005]FIG. 1 illustrates a device 100 including a PCB 104 to which is
attached a WL-CSP 108 by a plurality of solder balls 112. When subjected
to a drop test, the device 100 is deformed due to the impact from a
mechanical shock. FIGS. 2 and 3 illustrate the device 100 during a drop
impact. As shown in FIGS. 2 and 3, depending on the orientation during
the impact, the PCB 104 may be bent upward or downward. The WL-CSP 108
attached to the PCB 104 tends to follow the deformation of the PCB 104,
which leads to uneven loading of the solder balls 212.

[0006]As WL-CSPs increase in complexity and functionality, the size of the
silicon die (not shown) in the WL-CSP 108 and I/O count also increase. As
the size of the silicon die (not shown) in the WL-CSP 108 increases, the
solder balls at the periphery are subjected to increased loading and
deformation because they are farther away from a neutral axis 216. An
increase in the thickness of the silicon die (not shown) in the WL-CSP
108 also causes the WL-CSP 108 to become less compliant to bending,
resulting in deformation.

[0007]The device 100 may also be subjected to a thermal cycle test, which
is used to thermally cycle a semiconductor device between hot and cold
temperatures to determine the durability of the device. FIG. 4
illustrates the effect on the device 100 during a thermal cycle test.
Since the silicon die (not shown) in the WL-CSP 108 expands and contracts
at a much lower rate than the PCB 104 during a thermal cycle test, the
solder balls 112 at the periphery are subjected to high shear stress,
hence resulting in poor test reliability.

[0008]Furthermore, a recent trend toward smaller bump pitch of the solder
balls 112 has resulted in smaller diameter of the solder balls 112. A
smaller bump pitch of the solder balls 112 also results in smaller Under
Bump Metallurgy (UBM). Since the UBM opening defines the contact area of
the solder balls 112 to the silicon die (not shown) in the WL-CSP 108, a
smaller contact area lowers a threshold limit of the solder balls 112 to
withstand shear and tensile loads during the drop test and the thermal
cycling test.

[0009]Unlike a ball grid array (BGA) device that generally has some
redundant solder balls as dummy balls to improve the BGA device's drop
test and thermal cycling reliability, a WL-CSP device's solder balls are
all functional because the WL-CSP device is not designed to accommodate
high I/O counts like a BGA device. Consequently, the drop test and
thermal cycle test performance of the WL-CSP device cannot generally be
improved by adding redundant solder balls.

SUMMARY OF THE DISCLOSURE

[0010]A chip scale package (CSP) device includes a CSP having a
semiconductor die electrically coupled to a plurality of solder balls.
The CSP is housed in a can having an inside top surface and one or more
side walls defining a chamber. The CSP is attached to the inside top
surface of the can. The CSP may be a Wafer-Level CSP or any other type of
CSP.

[0011]The can is made from a metallic substance or a non-metallic
substance. The side walls of the can are spaced from the CSP by a
selected distance. The inside top surface of the can may be square,
rectangular or any other shape. In one implementation, an opening is
formed on a top surface of the can. The can enhances a drop test
performance and a thermal cycle test performance of the CSP device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]For a more complete understanding of the features, example
embodiments and possible advantages of the present invention, reference
is now made to the detailed description of the invention along with the
accompanying figures and in which:

[0013]FIG. 1 illustrates a device including a printed circuit board to
which is attached a WL-CSP;

[0014]FIGS. 2 and 3 illustrate a device during a drop impact;

[0015]FIG. 4 illustrates a device during a thermal cycle test;

[0016]FIG. 5 illustrates a device in accordance with one embodiment;

[0017]FIG. 6 illustrates a plan view of a CSP device with a metal can
attachment in accordance with one embodiment;

[0018]FIG. 7 illustrates a perspective view of a CSP device attached to a
metal can;

[0019]FIG. 8 illustrates an embodiment in which two CSPs are attached to a
single metal can;

[0020]FIG. 9 illustrates another embodiment in which two CSPs are attached
to a single metal can;

[0021]FIG. 10 illustrates another embodiment in which a CSP is attached to
a metal can having an opening;

[0022]FIG. 11 illustrates a device built by attaching the embodiment shown
in FIG. 10; and

[0023]FIGS. 12 and 13 illustrate an exemplary method of manufacturing a
CSP device with a metal can attachment in accordance with one embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024]FIG. 5 illustrates a device 500 in accordance with one embodiment.
The device 500 includes a WL-CSP 504. The WL-CSP 504 includes a silicon
die 506 on which a metal layer 510 is formed. A plurality of solder balls
512 are attached to the metal layer 510 and are electrically coupled to
the silicon die 506.

[0025]A can 516 in the form of an open box has a top member 528 and a side
member 524. The can 516 is placed over, and attached to, the WL-CSP 504.
The can 516 and the WL-CSP 504 are then attached to a PCB 508. As shown
in FIG. 5, the WL-CSP 504 is attached to the PCB 508 via the solder balls
512. The PCB 508 supports the WL-CSP 504 through the solder balls 512 and
supports the can 516 through the side member 524. The inside top 520 of
the can 516 is attached to the WL-CSP 504. Hence, the WL-CSP 504 is
enclosed in a cavity 528 defined by the can 516 and the PCB 508.

[0026]The side member 524 of the can 516 is spaced from the WL-CSP 504 by
a separation distance D. The separation distance D may be varied if
desired. In one implementation, the separation distance D may be zero, in
which case the side member 524 touches the WL-CSP 504. While the side
member 524 is shown to be perpendicular to the top member 528 of the can
516, it will be understood by those skilled in the art the side member
524 may be at other desired angles with respect to the top member 528.
The can 516 is made from a metal substance or alternatively from a
suitable non-metallic substance, such as a composite, a plastic or glass.

[0027]It will be understood by those skilled in the art that while the
device 500 is implemented with a WL-CSP, other types of CSPs may also be
used with the can 516. It will also be understood that BGA type packages
in which a silicon die is encapsulated in an encapsulating compound may
also be attached to a can to improve drop test and thermal cycle test
performances. Also, any other type of semiconductor die may used instead
of a silicon die.

[0028]Referring back to FIG. 5, the can 516 alleviates shear and tensile
stress experienced by the solder balls 512 at the edges or periphery
during a drop test. The can 516 through its side 514 absorbs some of the
shear and tensile stress generated during the drop test, thus improving
the device 500's drop test performance. Likewise, the can 516 alleviates
shear and tensile stress experienced by the solder balls 512 at the edges
during a thermal recycle test, thus improving the device 500's
performance during the thermal recycle test.

[0029]Furthermore, the can 516 adds to the rigidity of the device 500,
thus preventing the device 500 from deforming excessively during a drop
test. Because a portion of the shear and tensile stress is absorbed by
the can 516 during the drop test, the solder balls 512 at the edges or
the periphery are subjected to lesser out-of-plane deformation compared
to a CSP device without a can attachment.

[0030]Moreover, the presence of the can 516 restricts the movement of the
silicon die 506 with respect to the PCB 508 during a thermal cycle test.
For example, the thermal coefficient of expansion value of the PCB is
much closer to the thermal coefficient of expansion value of a metal can
(e.g., copper metal can) than the thermal coefficient of expansion value
of the silicon die 506 in a WL-CSP. Consequently, the can 516 (i.e., a
metal can) expands and contracts at a closer rate to the rate of
expansion and contraction of the PCB 508, thus subjecting the solder
balls 512 at the edges to be subjected to less shear deformation and
stress. Also, the WL-CSP 504 with the can 516 attachment improves the
device 500's drop test performance and thermal cycle test performance
without requiring redundant solder balls or other expensive solutions
such as utilizing a redistributed line (RDL).

[0031]FIG. 6 illustrates a plan view of the WL-CSP 504 attached to the can
516. The WL-CSP 504 resides inside the cavity 524 of the can 516. While
the can 516 is illustrated as having a square shape, it will be
understood by those skilled in the art that the can 516 can take other
shapes (e.g., rectangular, round). FIG. 7 illustrates a perspective view
of the WL-CSP 504 attached to the can 516.

[0032]FIG. 8 illustrates an embodiment in which two CSPs 804 and 808 are
attached to a single can 816. Thus, the two CSPs 804 and 808 reside in
the cavity of the can 816. The CSPs 804 and 808 may be WL-CSP or any
other type of CSPs. It will be understood that more than two CSPS may be
attached to a single can. The embodiment of FIG. 8 enables multiple CSPs
to have enhanced drop test and thermal cycle test performances. Also, the
size of the can 816 may be enlarged to shield selected areas of a PCB
(not shown) from electromagnetic interference.

[0033]FIG. 9 illustrates yet another embodiment in which two CSPs 904 and
908 are attached to a single can 912 but the CSPs 904 and 908 are
separated from each other by an isolation wall 916. The isolation wall
916 provides EMI isolation of the enclosed CSPs. The CSPs may be WL-CSPs
or any other type of CSPs. It will be understood by those skilled in the
art that a single can may accommodate more than two CSPs by having
additional isolation walls.

[0034]FIG. 10 illustrates yet another embodiment in which a CSP 1004 is
attached to a can 1016 having an opening 1020. The opening 1020 is formed
about the center of the can 1016.

[0035]FIG. 11 illustrates a device 1100 built by attaching the embodiment
of FIG. 10 to a PCB 1104. The opening 1020 provides additional
flexibility to the can 1016 enabling it to bend during a drop test. This
additional flexibility due to the opening 1020 enables the device 1100 to
withstand greater shear and stress, thus improving the device 1100's drop
test and thermal cycling test performances.

[0036]There are several advantages of the above-described embodiments. The
CSP devices with the can attachment exhibit superior drop test thermal
cycle test performances compared to other designs. Various computer
simulations were run for a WL-CSP with a metal can attachment of
3.6×6×0.6 mm, F 8×8, 0.4 pitch, 0.25 mm ball, SAC405
solder. The simulation results indicate that the WL-CSP with the metal
can attachment reduces peeling stress in solder balls by approximately a
factor 2×. Also, the metal can attachment increases characteristic
life of a WL-CSP by a factor of 6× compared to other designs. The
metal can attachment to the WL-CSP also functions as a heat sink, thus
dissipating heat from the silicon die in the WL-CSP. Also, the metal can
provides EMI isolation between a WL-CSP and other electronic component in
a circuit board, thereby improving the electrical performance of the
WL-CSP. The metal can attachment to the WL-CSP makes it unnecessary for a
separate EMI shield, which reduces the overall cost of the device.

[0037]FIGS. 12 and 13 illustrate an exemplary method of manufacturing a
CSP device with a metal can attachment in accordance with one embodiment.
As shown in FIG. 12, CSP devices 1204, 1208 and 1212 are each attached to
a respective chamber 1220, 1224 and 1228 formed on a metal frame 1232.
The chambers are each sized to house a CSP device. The metal frame 1232
containing the CSP devices is then sawed or diced along the lines L1-L2
to create singular devices each capped with a metal can. A CSP device
1300 with a metal can attachment created from the process shown in FIG.
12 is illustrated in FIG. 13.

[0038]It will also be appreciated that one or more of the elements
depicted in the drawings/figures can also be implemented in a more
separated or integrated manner, or even removed or rendered as inoperable
in certain cases, as is useful in accordance with a particular
application.

[0039]As used in the description herein and throughout the claims that
follow, "a", "an", and "the" includes plural references unless the
context clearly dictates otherwise. Also, as used in the description
herein and throughout the claims that follow, the meaning of "in"
includes "in" and "on" unless the context clearly dictates otherwise.

[0040]The foregoing description of illustrated embodiments of the present
invention, including what is described in the Abstract, is not intended
to be exhaustive or to limit the invention to the precise forms disclosed
herein. While specific embodiments of, and examples for, the invention
are described herein for illustrative purposes only, various equivalent
modifications are possible within the spirit and scope of the present
invention, as those skilled in the relevant art will recognize and
appreciate. As indicated, these modifications may be made to the present
invention in light of the foregoing description of illustrated
embodiments of the present invention and are to be included within the
spirit and scope of the present invention.

[0041]Thus, while the present invention has been described herein with
reference to particular embodiments thereof, a latitude of modification,
various changes and substitutions are intended in the foregoing
disclosures, and it will be appreciated that in some instances some
features of embodiments of the invention will be employed without a
corresponding use of other features without departing from the scope and
spirit of the invention as set forth. Therefore, many modifications may
be made to adapt a particular situation or material to the essential
scope and spirit of the present invention. It is intended that the
invention not be limited to the particular terms used in following claims
and/or to the particular embodiment disclosed as the best mode
contemplated for carrying out this invention, but that the invention will
include any and all embodiments and equivalents falling within the scope
of the appended claims. Thus, the scope of the invention is to be
determined solely by the appended claims.